| Summary: | <p>Abstract</p> <p>Background</p> <p>Acquiring a highly stable photonic plasmid in transformed <it>Salmonella Typhimurium </it>for use in biophotonic studies of bacterial tracking <it>in vivo </it>is critical to experimental paradigm development. The objective of this study was to determine stability of transformed <it>Salmonella Typhimurium </it>(<it>S. typh</it>-lux) using three different plasmids and characterize their respective photonic properties.</p> <p>Results</p> <p>In presence of ampicillin (AMP), <it>S. typh</it>-lux with pCGLS-1, pAK1-lux and pXEN-1 plasmids exhibited 100% photon-emitting colonies over a 10-d study period. Photon emitters of <it>S. typh</it>-lux with pCGLS-1, pAK1-lux and pXEN-1 without AMP selection decreased over time (P < 0.05), representing only 11 ± 1%, 35 ± 1% and 43 ± 1%, respectively, of original photon emitting properties of the bacterial population by d 10. Photonic emissions were positively correlated with bacterial concentration (P < 0.05) for pAK1-lux, pCGLS-1 and pXEN-1 (r = 0.96, 0.98 and 0.82, respectively). When stratified by high, medium and low density bacteria concentrations, photonic emissions for high density populations containing pAK1-lux, pCGLS-1 and pXEN-1 resulted in differences of photonic emissions across a range of bacterial concentrations (1 × 10<sup>7 </sup>to 1 × 10<sup>9 </sup>CFU, P < 0.05) with positive correlations (P < 0.05) of (r = 0.72, 0.46 and 0.72, respectively). The correlation of photonic emissions with bacterial concentrations for samples with medium and low density bacteria (pAK1-lux, pCGLS-1, and pXEN-1 plasmids) imaged in tubes were also positively correlated (medium; r = 0.69, 0.49, 0.46, low; r = 0.90, 0.71, 0.68, respectively; P > 0.05); although photonic emissions across a range of bacterial concentrations were not different (1 × 10<sup>4 </sup>to 1 × 10<sup>6 </sup>CFU, P > 0.05). For very low density bacterial concentrations imaged in 96 well plates photonic emissions were positively correlated with bacterial concentration (P < 0.05) for pAK1-lux, pCGLS-1, and pXEN-1 plasmids (r = 0.99, 0.99, and 0.96, respectively), and photonic emissions across a range of bacterial concentrations (1 × 10<sup>3 </sup>to 1 × 10<sup>5 </sup>CFU) low to high were different in the 96-well plate format (P < 0.05).</p> <p>Conclusion</p> <p>These data characterize photon stability properties for <it>S. typh</it>-lux transformed with three different photon generating plasmids that may facilitate real-time <it>Salmonella </it>tracking using <it>in vivo </it>or <it>in situ </it>biophotonic paradigms.</p>
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